Induction heating apparatus



Feb. 12, 1946. R. J. STANTON INDUCTION HEATING APPARATUS Filed Feb. 10, 1945 Z 3 1H 2 w, m; I 1 I I 5 E 1 i v-7 7 Q mmw/7 m ml mm will w cbs:::::::::

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' Patented Feb. 12, 1946 2,894,944 INDUCTION HEATING APPARATUS Robert J. Stanton, Brooklyn, N. Y., assignor to Induction Heating Corp., New York, N. Y., a corporation of New York Application February 10, 1945, Serial No. 557,211

4 Claims. (Cl. 219-13) This invention relates to induction heating apparatus and more particularly to so-called inductors or Work coils" for applying the high frequency field to the objects to .be heated.

For simplifying and expediting. operations in volume production work, it is often desirable to heat a plurality of separate portions of an object or a plurality of adjacent objects simultaneously by the use of a single fixture or inductor. Where the objects, or different portions of the same object are of a construction such that all may properly be heated to about the same extent, this may be conveniently done by placing successive portions of the same inductor, connected in series, in positions adjacent the several areas of the object or objects to be heated as is disclosed for example in the patent to Dravneek, No. 2,353,130, granted July 11, 1944, reference to which is hereby made. In some cases, however, it is desirable to apply heat at a different rate to different portions of'a single object or of adjacent objects. For example, an object may be formed with one portion comprising a considerable mass of metal, and with another portion having a relatively much lighter mass which may be in the'form of a small lug or rod or other protuber- In that case, if both portions are placed adjacent successive series connected portions of a single inductor, difficulties arise due to the difference in the two masses to be heated. That is, either the lighter mass will be overheated befor the heavier mass approaches the desired temperature,

or if the power is cut off upon the lighter mass reaching the desired temperature, then the heavier mass may not be heated enough. Any attempts to use a single inductor for this double purpose, by increasing the coupling space between the inductor and the lighter mass, to minimize the heating of the latter, will involve uncertainties and possibly substantial power losses as a result of the induction effects occurring with such wider spacing.

According to the present invention, th above noted difficulties are overcome by providing a single inductor device having two portions, one for heating the larger mass and the other for heating the lighter mass, these two portions being so connected in parallel that the second inductor portion taps off current from the main inductor at a lower voltage, with the consequence that less current flows through the second inductor portion and both masses may be heated to the-particular extent desired. According to the invention, a simple and unitary inductor fixture is provided for the two purposes in such form that adjacent portions of the same object or of adjacent objects. may be supplied with substantially different amounts of heat as required, the two heating operations being accomplished substantially as conveniently and quickly as if but a single heating operation were bein performed.

Various further and more specific objects, features and advantages of the invention will more clearly appear from the detailed description given below taken in connection with the accompanying drawing which forms a part of this specification and illustrates merely by way of example,

a preferred form of the invention. The invention consists in such novel features, arl'ahgements and combinations-of parts as may be shown and described in connection with the apparatus herein disclosed.

In the drawing:

Fig. l is a plan view. of a preferred and simple form of inductor made in accordance with the invention, and showing how same may be used for heating, for example, portions of a large cylindrical mass and for simultaneously heating an extension portion on the object, of relatively small mass; and

Fig. 2 is a side view of the device of Fig. 1.

Referring to the drawing more specifically, portions of a high frequency step-down transformer are indicated at iii, the secondary terminals of the transformer being shown at H, II. In this case a one-turn work coil I3 is constructed of a generally ring shape and arranged to be supported if desired directly upon and by the transformer secondary terminals. Starting at the terminals n, n, a divided base portion of the inf ductor is formedwith a pair of attaching lugs as at l4, IS. A heavy conductor comprising, for example, a rigid bar of copper of rectangular cross section may have an angular portion as at It brazed to the lug H, such bar extending out as at H to the ring portion per se of the inductor,

then extending around such portion as at It and back to another terminal connecting bar It, which terminates at an angular portion 20 and at terminal lug II.

In order to properly cool the parts during use, the portions II, It and it may be formed with cooling fluid cavities as indicated at 2 I, these cavities communicating in series, starting at one supporting terminal and passing around to the other supporting terminal, the terminal ends of the cavities being connected to inlet and outlet fluid pipes as at 22 and 23.

The structure comprising the parts i1, i8 and I9 and the supporting terminal structure therefor may be initiall made if desired as several separate parts which are welded, brazed or otherwise secured together to form the rigid integral piece as shown. The cooling fluid cavities if desired may be drilled'through these parts before thesame are Joined and in the case of the ringshaped portion, before such portion is bent to the ring-like form. Or if preferred, the cooling fluid cavities may be machined into the parts or into the assembled construction in the form of a groove which may be later covered over by welding in place a. suitable strip so as to leave the fluid cavity unobstructed but properly sealed against leakage.

As to other features and details of construction of the portions thus far described, and the uses thereof, principles may be followed the same as disclosed in the above-mentioned Dravneek patent.

The ring-like portion I8 is here shown as extending around an object at a region thereof embodying a relatively heavy mass, requiring a relatively heavy high frequency current to heat the same within the desired short time. The object 25 is shown as also including an extension portion 26 of smaller mass, which may be either integral with or separable from the main body and which, due to its smaller mass, may be quickly heated to the desired temperature, for example, for hardening purposes, by the use of a substantially smaller current than required for heating the main mass. For this latter purpose an inductor portion 21 is provided for encircling the member or portion 26, and this inductor portion has its ends or connection terminals 28 and 28 affixed respectively at spaced points as at 30, Si to the main inductor portion 18. As shown, the inductor portion 21 and its terminals may be formed of hollow metal tubing so as to provide therethrough a cooling fluid conduit, the ends of which as indicated at 32 in Fig. 2, are brought into communication with the cooling fluid flowing through the cavity within the portion l8. The tube portions 28 and 29 may be secured at points 30 and 34 as by brazing or in any other suitable way to insure proper communication and sealing of the fluid conduits against leakage.

Assuming that a high frequency current is applied from the transformer secondary to the terminal connections of the device, for example, a current of several hundred thousand cycles per second frequency and with a voltage such that the voltage between the bars ll and 15 will be, for example, 150 volts, then it will be apparent that the voltage drop across the points 30, 3! will be of substantially lesser value, depending upon the proportion of the ring-like part I8 which is connected in parallel with the portions 21, 28 and 29. It will be apparent that by proper selection of the circumferential spacing for the points 30 and 3 I, one may secure a voltage drop across the portions 21, 28 and 29 which will amount of any predetermined desired proportion of the voltage drop across ,the terminals of the main inductor portion l8. For example, if as viewed in Fig. 1, point 30 is moved upwardly, then the voltage drop across the supplemental inductor 21 will increase, thereby increasing the current and the resulting heating effect on the protuberance 26. Conversely, by bringing the points 30 and 3! closer together, the heating effect from the supplemental indicator 21 may be decreased.

While in the form shown, the main inductor l8 and the supplemental inductor portion 21 are both shown as circular, it will be understood that the invention is equally applicable where, due to the shape of the parts to be heated, the inductor portions are formed otherwise than as circular or arcuate, but so as to maintain the desired small coupling space with respect to the surfaces of the objects to be heated. Also it will be understood that the principles of the invention may be applied to inductors of types having several cavities adapted for simultaneously heating several separate objects such as may be done with the inductors of the above-mentioned Dravneek patent. In that case either some or all of the cavities for the separate objects may be accompanied by suitably arranged supplemental inductors connected in parallel with adjacent portions of the accompanying main inductor.

While the invention has been described in detail with respect to particular preferred examples, it will be understood by those skilled in the art after understanding the invention, that various changes and further modifications may be made without departing from the spirit and scope of the invention, and it is intended therefore in the appended claims to cover all such changes and modifications.

What is claimed as new and desired to be secured by Letters Patent is:

1. An inductor for applying a high frequency electromagnetic field to objects to be heated, comprising a substantially rigid conductor for substantially encircling a. portion of an object, a pair of closely spaced connection terminals secured respectively to the ends of said conductor, a second substantially rigid conductor for applying a field to another portion of the object, th ends of said second conductor respectively being fixed to the first conductor at predetermined spaced points on the latter, at least one of said points being spaced from the region of said terminals, whereby the voltage drop across saidsecond conductor will be less than that across the first-named conductor, by a predetermined proportion.

2. An inductor for applying a high frequency electromagnetic field to objects to be heated, comprising a substantially rigid conductor for substantially encircling a, portion of an object, a pair of closely spaced connection terminals secured respectively to the ends of said conductor, a second substantially rigid conductor for applying a field to another portion of the object, the ends of said second conductor respectively being fixed to the first conductor at predetermined spaced points on the latter, at least one of said points being spaced from the region of said terminals, whereby the voltag drop across said second conductor will be less than that across the first-named conductor, by a predetermined proportion, said terminals and conductors being formed with communicating cooling fluid cavities, the conductor cavities being connected in parallel and arranged whereby fluid may enter through one terminal and leave through the other after passing through the conductor cavities.

3. In combination, a generally ring-like inductor for applying a high frequency electromagnetic field to an object to be heated, and a supplemental ring-like inductor for applying such a field to another portion of the object or an adjacent object, said supplemental inductor being mounted upon and connected in parallel with a predetermined portion only of the first-named inductor to thereby tap off, at a reduced voltage,

a portion of the current supplied to said first inductor.

4. In combination, a high frequency inductor for extending around an object to be heated, a supplemental inductor for extending around another portion of the object or an adjacent object, said supplemental inductor having its terminals connected at spaced points along said firstnamed inductor, said points being so chosen that the supplemental inductor is connected in parallel with a predetermined portion only of the first inductor.

' ROBERT J. STANTON. 

